This invention relates to a method and system or using flight plan information to produce a model and then evaluating the modeled airplane flight path in view of terrain information to produce an alert for portions of the flight path model in which potentially inadequate ground clearance may occur.
Current flight management systems accept flight plan information and use this information in the piloting of aircraft. Many such systems are capable of outputting this information in digital form for use by other flight instruments. Various interface and data format standards for the transmission of such digital information have been developed and implemented. One such form of digital communication is the unidirectional communication via a wire pair data bus according to the ARINC 429 interface standard. The flight management system may have two or more such interfaces with one dedicated to data output and another to data input. Another such standard is ARINC 629, which allows higher speed, bidirectional data transmission across a bus. Data can be transmitted through such an interface in serial form in accordance with the ARINC 702 or proposed 702(a) or other standard. Under the ARINC 702 standard, for example, data is transmitted in 32 bit units. The first eight bits of the unit are the label, identifying the type of data. Flight plan information sent over the data bus may be read by any equipment interfaced to the bus, and the information contained in the latter 24 bits of the unit may be identified as to type by the eight bit label. The construction and operation of such interfaces and the transmission of such data according to protocols such as ARINC 702 are known in the art. It is also within the ability of those skilled in the art to buffer such data, translate data between different data protocols and so forth.
Current flight management systems presently include a screen, and properly labeled data transmitted to such flight management systems can frequently be displayed on such screens. In addition, the flight instrumentation may include other screens that can be sent data over a data bus, or which can be switched to receive text data, images or image overlays. Interfacing an instrument to such other screens is within the ability of those skilled in the art of the design of aircraft instrumentation. One such screen on which a flight instrument may display information may be a weather radar screen. It is known to provide switching capability to disable the sending of video signals or data from a weather radar to the weather radar screen and allow the display of video signals from such other instrument on the weather radar screen in lieu thereof. Likewise, some aircraft include multipurpose displays on which text and/or images from an instrument may be displayed, and the interfacing of instruments to such displays and their associated electronics is known in the art.
Finally, the provision of text, image, indicator light, tone, synthesized or digitized voice annunciation in response to determination of conditions requiring an alert, caution or warning are known in the art.
The flight plan information for a flight between two airports may be entered into the flight management system or other avionics in many forms, but commonly is represented by a series of flight waypoints with the initial waypoint being the departure airport and the final waypoint being the destination airport. The direct path to a waypoint is a leg, and taken together, the legs define the intended flight plan of the aircraft. Some current and planned flight management systems are capable of receiving the input of and storing about 99 waypoints. The waypoints represent a series of locations along the flight plan, and other information such as altitude constraint and waypoint identifier may be associated with specific waypoints. The flight plan information may also include required navigation performance or flight phase information.
The altitude constraint information may be an actual altitude or a qualified altitude. Qualifiers to altitude data would be at or above, above, at or below and below. For example, an at or above 8,000 feet altitude constraint would indicate the intent that the aircraft be at an altitude at the waypoint which was no less than 8,000 feet.
The waypoint identifier is a letter designation of up to five letters associated with a specific location. For example, the identifier for an approach waypoint into Seattle ANVIL. The waypoint identifier may represent the location of an airfield, radio navigation aid or other selected location. Many such waypoints are identified by such identifiers on air navigation charts. While the flight crew could enter the flight plan information by keying in the latitude, longitude and other information on the keypad of the flight management system or other device, it is frequently more convenient and less likely to cause error to allow entry of the waypoint by keying in the identifier.
Required navigation performance data, which could be provided by a flight management system as part of the flight plan information, would indicate the maximum allowable deviation from the flight path. This data may be represented by the minimum allowable deviation from a point along the flight plan which is allowed. Deviation from the flight path may occur due to a variety of factors including the lack of exact aircraft position information. Such deviation may result, for example, from drift in an inertial navigation system, limitations in the precision of a global positioning system, or from other instrument accuracy or aircraft operation factors. The required navigational performance may vary depending on aircraft flight parameters. For example, the aircraft must be flown with enhanced positional precision and may be allowed to approach terrain more closely both laterally and vertically during a landing approach than may be appropriate during the en route phase of the flight.
In addition to or in lieu of required navigation performance data, a flight management system may also provide flight phase information in conjunction with the other flight plan information. Although many different categories of flight phase information could be provided, three categories for flight phase are the approach/departure phase, which may generally be defined as within six miles of the approach or departure airport, the terminal phase, which would be the area outside the approach departure phase area but within fifteen miles of the airport, and the en route phase, which would apply to the portions of the flight outside the approach/departure and terminal areas.
While errors in the entry of flight plan information are not common, they are known to occur. Confusion between waypoint identifiers, miskeying of information, such as pressing the xe2x80x9c0xe2x80x9d key too few times, resulting, for example, in the entering of an altitude constraint of 2000 feet rather than 20,000 feet, or misreading latitude and longitude figures from a chart may result in a flight path that could, and have, contributed to a subsequent controlled flight into terrain. Unfortunately, it is not practical for flight crew members to attempt to check the flight path manually. This might require the plotting of the intended flight path on a map with contour information and then examining the contour information along the entire flight path. Moreover, deviations from the intended flight plan often occur during the flight. Such changes would require further plotting and checking of maps and contour information while en route.
Present and proposed ground proximity warning systems and terrain avoidance warning systems use a variety of flight configuration, position, altitude, velocity and other information to detect and warn of dangerous flight situations. Some such systems may include terrain data, including terrain models, and may use such models, for example, in the terminal area, to define altitudes below which an aircraft in a given configuration should not descend. Such systems, however, do not provide pre-checking of the intended flight path as determined from the flight plan information in order to provide an advanced warning which would allow for correction or modification of flight plan data. Rather, the violations of selected flight performance criteria result in an alert only as the terrain is being approached.
Terrain data is presently available for much of the surface of the earth. Typically, such data is presented as a grid or series of grids with grid elements representing areas of, at maximum, 30 arc seconds (30xe2x80x2) of longitude by 30xe2x80x3 of latitude. At the equator, 30xe2x80x3 of longitude and 307 of latitude represent an approximate square of 3038 feet, or about one half nautical mile (0.5 nm), on a side. As you approach either the north or south pole, of course, 30xe2x80x3 of longitude continues to correspond to 3038 feet or about 0.5 nm, but at 45xc2x0 latitude, 30xe2x80x3 of latitude represents only about 2148 feet. Thus, a grid element at this latitude would be generally rectangular.
For certain regions, the terrain data is provided in an enhanced resolution form. For example, within 15 nm of selected airports, the grid elements are provided at a resolution of 15xe2x80x3, corresponding to approximately 0.25 nm of longitude. Within 6 nm of selected airports, moreover, resolutions of 6xe2x80x3 or about 0.10 nm of longitude are provided. As with the 30xe2x80x3 data mentioned above, of course, the exact dimensions of the 15xe2x80x3 and 6xe2x80x3 grid elements varies according to the latitude.
The data for each grid element is representative of the longitude and latitude of the center of the grid and of the maximum terrain altitude within the grid. The number of arc seconds of resolution of the grid elements is identified in conjunction with the grid, so the location of the corners of the grid could be calculated from the center point. The data is not provided with any indication of the location of the highest point of the terrain within a grid element. Altitude data is generally accurate to within about 30xe2x80x3.
The present invention provides a method and system for receiving output signals from a flight management system and other flight instrumentation and using terrain data to identify flight path intent alert conditions. The terrain data may be in the form of grid elements as described above. However, other methods of representing terrain data could be used within the scope of the invention. Such methods may include topological descriptions of the surface of the earth as a series of contiguous triangles or other planar geometric members or as a mathematical model. It is only necessary for purposes of the present invention that terrain data be available for determining the altitude of terrain at a plurality of locations along a flight path with a known resolution.
In the present invention, a flight path intent alert system is provided which uses flight plan information obtained from the flight management system or otherwise. To the extent that the flight plan data permits, the flight plan data is used to generate an intended flight path. The intended flight path generally corresponds to a direct flight from the longitude, latitude and altitude of the first or current waypoint of a leg to the latitude, longitude and altitude of the next waypoint.
On the ground, the flight path may be modeled using the airport as the current waypoint and continuing to the last of the entered waypoints. In the air, the aircraft location and altitude, as obtained from the flight management system or other instrumentation interfaced to the flight path intent alert system may be used as the current waypoint, and the flight path may be modeled as extending directly to the next waypoint in the series of waypoints. A determination of whether the aircraft is on the ground or in the air may be made by any of a number of methods, including the use of a threshold airspeed above which the aircraft will be presumed in flight or the existence of pressure above a minimum pressure on a load cell associated with the landing gear of the aircraft, such higher pressure indicating that the aircraft is on the ground, and a lower pressure or the absence of pressure indicating that the aircraft is in flight.
If the aircraft is on the ground, the presence of flight path intent alert conditions is determined for all of the legs of the flight path for which sufficient data is available and the nearest alert annunciated, and the flight path intent alert status will remain static until an indication is received that the aircraft is in the air or until the flight plan information is modified. Once the aircraft is airborne, the aircraft position and altitude will serve as the current waypoint for flight plan leg which is actually being flown.
Before takeoff or during the flight, the flight plan information may be modified by the flight crew. If this occurs, the flight path intent alert system must recognize such modification and check again for flight path intent alert conditions. Such modifications may eliminate existing alert conditions or create new alert conditions.
If required navigational performance data is present, such data can be used to provide a horizontal tolerance around the intended flight path. If the terrain data for positions falling along the flight path or within the horizontal tolerance to either side of the flight path indicates an altitude that is greater than or equal to the altitude of the aircraft at that point along the flight path, an alert condition will be determined to exist. A vertical tolerance may also be provided and may be used to provide a determination of an alert condition if the terrain altitude comes to within or exceeds the altitude of the aircraft at a point along the flight path or within the horizontal tolerance to either side of the flight path.
If required navigational performance data is absent, but flight phase data is present in the flight plan information, this information may be used to calculate a horizontal and, possibly, vertical tolerance for the flight path. Tighter tolerances could be provided for approach/departure flight phases, somewhat broader tolerances could be used for the terminal flight phase and the tolerances could be further broadened for flight in an en route flight phase. The tolerances corresponding to each flight phase may be predetermined and stored in the flight path intent alert system in a table or otherwise.
In the event that neither required navigational performance data nor flight phase data is available, a default horizontal and possibly vertical tolerance could be provided. Such tolerance may be a predetermined single value, or could be a set of predetermined values from which the tolerance or tolerances would be chosen, for example, based on parameters such as altitude, airspeed or the like or combinations thereof, or could be calculated dynamically based on a formula.
Where the terrain data is represented as discussed above as a grid with grid elements of an indicated number of arc seconds of longitude and latitude, one half of such dimensions may be used as an increment value and the terrain data may be examined for the latitude, longitude and altitude corresponding to that of the intended flight path at discrete points therealong as defined by latitude, longitude and altitude. The altitude may advantageously be determined from the distance between two waypoints, the altitude constraint for each such waypoint and the length of an increment. If there are 100 increments between the two waypoints, and if the second of the two waypoints has an altitude constraint 5000 feet greater than that of the first of the two waypoints, and if the location being considered is at a distance of 20 increments from the first of the waypoints, then the altitude that may be used for the position of the 20th increment along the intended flight path could be taken as the altitude constraint associated with the first waypoint increased by 20 increments multiplied by 50 feet per increment (5000 feet divided by 100 increments), or 1000 feet. Flight plan intent alert conditions may be determined for each such point and for points to either side thereof out to the lateral tolerances. These points may likewise be spaced apart by not more than a distance equal to half the resolution of the terrain data out to the horizontal tolerance.
Some flight plan data may be insufficiently detailed to permit its use as an altitude. The altitude component of 8000 feet associated with an altitude constraint of xe2x80x9cabove 8000 feetxe2x80x9d may safely be used, as flight above this level merely provides more terrain clearance than might be expected by using an altitude of 8000 feet. An altitude constraint that is given in the form of xe2x80x9cat or belowxe2x80x9d or xe2x80x9cbelowxe2x80x9d a specific altitude cannot be used for determining the intended altitude of the aircraft at that location because there is no indication as to how much below such altitude the pilot may intend to fly. In such case, the waypoint should be considered not to have an associated altitude constraint. Similarly, there may be no altitude constraint associated with a waypoint. In such case, it may not be possible to model the flight path for a leg accurately. In such case, use of the terrain data along the leg to such waypoint to calculate flight path intent alerts may be omitted. However, during flight, once such waypoint is reached, if the next waypoint has a useable altitude constraint, the present position and altitude of the aircraft may be used as the current waypoint of the leg, and the determination of the existence of flight plan intent alert conditions may be made for the leg between the aircraft""s position and that waypoint.
A variety of methods may be used to provide flight path intent alerts to the flight crew. When a flight path intent alert condition is determined, a text alert could be generated on the flight management system screen, if it is so addressable. Likewise, if the flight path intent alert system is interfaced to a multipurpose display or weather radar display such that it can display images and/or text, an alert could be generated on such displays. Alerts could also be provided by a variety of known means, such as by having a light, tone or voice alert generated in manners known in the art.
One form of advantageous method of displaying flight path intent alerts would be via visual presentation of the flight path with associated displays of information and flight path intent alert graphics. One two dimensional representation of the flight path would be a side view, with the waypoints with useable altitude constraints represented as a series of points or vertical lines indicative by their position from the bottom of the screen, for points, or the extent to which they extend upward from the bottom of the screen, of the altitude constraint at the waypoint. Each leg for which current and next waypoint have useable altitude constraint data might be represented as a line drawn between the points or tops of the lines representative of the waypoints. An alert graphic and/or message could be displayed at any points along such lines at which a flight plan intent alert condition was detected. Lines representative of the intended flight plan would not be extended from or to waypoints for which useable altitude constraint information is not available. Terrain altitude could be indicated across the screen by vertical lines representative of the maximum altitude determined for locations along the flight path and within the horizontal tolerance around it, thus presenting a representation of an approximation of the terrain over which the airplane passes. Alternatively, a curve representative of terrain altitude versus flight plan position could be drawn across the screen and the area under the curve could be filled with a color representative of terrain. The alert graphics would thus be supplemented by a general indication of terrain clearance or lack thereof under the intended flight plan.
An overhead view or perspective view could likewise be presented. For these views, the terrain contour could be represented by shading or color, changes, and the intended flight path, again with missing segments where useable altitude constraints are absent, could be presented. Flight path intent alert graphics could be used to identify locations along the intended flight path at which alert conditions were determined to exist. For any of the displays, scrolling could be provided so that the flight crew could examine the entire intended flight path without the necessity of scaling the entire intended flight path to fit on the display at one time.